Embodiments relate to a semiconductor device including a buried gate, and particular embodiments relate to a semiconductor device configured to reduce mechanical stress caused by a nitride film by subtracting the volume of the nitride film from a capping insulation film formed over a buried gate.
Generally, a semiconductor is a material that falls within an intermediate region between a conductor and a nonconductor from among materials affected by electrical conductivity. Although a semiconductor is similar to a nonconductor in a pure state, electrical conductivity of the semiconductor device is increased by impurity implantation or other manipulation. The semiconductor is used to form a semiconductor device such as a transistor through impurity implantation and conductor connection. A device that has various functions while being formed of a semiconductor element is referred to as a semiconductor device. A representative example of the semiconductor device is a semiconductor memory device.
A semiconductor memory device includes a plurality of transistors. The transistor has three regions, i.e., a gate, a source, and a drain. Electric charges are moved between the source and the drain according to a control signal (the magnitude of a voltage) input to the gate of the transistor. The charges between the source and the drain move through a channel region in accordance with the properties and operation of the semiconductor device.
Generally, a method for manufacturing the transistor includes forming a gate over a semiconductor substrate, and forming a source and drain by doping impurities over the semiconductor substrate located at both sides of the gate. A region between the source and the drain may be located below a gate, and is used as a channel region of the transistor. The transistor including a horizontal channel region has difficult to form a highly-integrated semiconductor device.
In order to solve the above-mentioned problem, there is proposed a three-dimensional (3D) transistor in which all or some parts of the gate are buried by etching a silicon substrate. In particular, a buried gate structure in which the gate is completely buried in the silicon substrate, has been used.
Generally, the buried gate structure uses a nitride film as a capping insulation film formed over the gate so as to implement gate isolation. However, when using the nitride film formed over the gate, cell-transistor characteristics (specifically, refresh characteristics) may be deteriorated due to mechanical stress caused by the nitride film.